Water relations of wallum species in contrasting groundwater habitats of Pleistocene beach ridge barriers on the lower north coast of New South Wales, Australia

Abstract

This study examined the water relations of sclerophyllous evergreen vegetation (wallum) on coastal sand barriers in eastern Australia. Many wallum species may be groundwater dependent, although the extent of this dependency is largely unknown. Twenty-six perennial tree, shrub and herb species were investigated in three groundwater habitats (ridge, open depression, closed depression). Pre-dawn and midday shoot xylem water potentials (ψx) were measured monthly between late autumn 2010 and late summer 2011. Pressure–volume curve traits were determined in mid- to late spring 2009, including the osmotic potential at full (π100) and zero (π0) turgor, and bulk modulus of elasticity (ε). Carbon isotope ratios (δ13C) were also determined in mid- to late spring 2009, to measure water-use efficiency (WUE). The species displayed a range of physiological strategies in response to water relations, and these strategies overlapped among contrasting growth forms and habitats. Linear relationships between osmotic and elastic adjustment were significant. A strong correlation between δ13C and distribution along the hydrological gradient was not apparent. Banksia ericifolia subsp. macrantha (A.S.George) A.S.George, Eucalyptus racemosa Cav. subsp. racemosa and Eucalyptus robusta Sm. displayed little seasonal variation in ψx and maintained a comparatively high pre-dawn ψx, and are therefore likely to be phreatophytic. Wetland vegetation in the lowest part of the landscape appeared to tolerate extreme fluctuations in water availability linked to a prevailing climatic pattern of variable and unreliable seasonal rainfall.

Abiotic correlates with diversity and distinctiveness in Sunshine Coast heathlands: Moisture, volcanic landscapes and patterned mounds

“…Consistently, water has been found to be a key factor driving distinctiveness of composition in other heaths in Australia (Benson, 1981;Keith et al, 2014;Martin & Specht, 2005;Specht, 1994;Williams & Clarke, 2006). Topography was associated with the vegetation patterning of wider lowland Sunshine Coast vegetation (Coaldrake, 1961) and in heaths in New South Wales (Griffith et al, 2003(Griffith et al, , 2004Griffith & Wilson, 2007). However, topography influences a range of plant resources including moisture and the water-table depth (Griffith et al, 2003(Griffith et al, , 2008Griffith & Wilson, 2007).…”

“…Topography was associated with the vegetation patterning of wider lowland Sunshine Coast vegetation (Coaldrake, 1961) and in heaths in New South Wales (Griffith et al, 2003(Griffith et al, , 2004Griffith & Wilson, 2007). However, topography influences a range of plant resources including moisture and the water-table depth (Griffith et al, 2003(Griffith et al, , 2008Griffith & Wilson, 2007). Some studies of Australian heath find geology to be associated with plant distribution (Benson, 1981;Myerscough & Carolin, 2014) and others find a weak relationship Sellan et al, 2019;Tsakalos et al, 2019).…”

“…However, the considerable overlap in vegetation composition between the moist and wet sites of the coastal lowlands was unexpected, and occurs despite the substrate. This overlapping species composition between moist and wet sites could be related to the temporary rise and fall of perched water tables in the coastal heath from local weather events, and the capacity of wetland vegetation to tolerate these extreme fluctuations (Coaldrake, 1961;Deane et al, 2017;Griffith et al, 2015). Co-occurrence and germination of wet and dry heath species has been observed in southern heaths with the capacity of species to survive depending on ongoing water conditions (Clarke et al, 1996;Griffith et al, 2004).…”

Soluble sugar drives plant leaf turgor, restricts plant growth, and regulates plant hydraulic capacity of Haloxylon ammodendron to different groundwater level

“…Access to groundwater plays an important role in determining plant function and survival in GDEs (Froend & Sommer, 2010;. Depth to groundwater (DGW) further influences leaf water relations, hydraulic properties, growth, productivity, survival, and species composition (Gries et al, 2003;Griffith, Rutherford, Clarke, & Warwick, 2015;Yang, Li, Li, & He, 2019;Zolfaghar et al, 2014). Plasticity in hydraulic architecture plays a central role in adapting to differences in water availability (Tyree & Ewers, 1991;Zolfaghar, Villalobos-Vega, Zeppel, & Eamus, 2015).…”